The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Artificial magneto-dielectric materials have a wide range of uses. The typical approach to manufacturing these materials is mixing conductive particles (for example, metallic fibers, flakes, spheres, etc) in a polymer matrix, such that the conductive particles are in a random orientation. For example, United States Patent Application Publication No. 2004/0104847 (to Killen et al) describes the use of an antenna dielectric incorporates magnetic particles into voids within the dielectric material. All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. The disadvantage of such materials is that these particles can create conductive clusters (for example, by contacting each other) and as a result exhibit high electro-magnetic losses and non-homogeneity. This restricts the use of such materials in applications such as electro-magnetic lenses for antenna applications, where low loss and uniformity (homogeneity) are critical requirements.
U.S. Pat. No. 8,518,537 (to Matitsine) discusses antennas having a dielectric material made from discrete units of dielectric material with conductive fibers and/or wires embedded within them. However, the use of essentially one-dimensional wires in such devices limits their dielectric permittivity, and requires the use of large numbers of individual units to provide an effectively isotropic effect. The resulting devices are therefore relatively large and inefficient. In addition, such devices do not permit control of magneto-dielectric properties.
United States Patent Application Publication No. 2012/0228563 (to Fuller et al) describes the use of composite materials for a variety of RF applications. The described composite materials include an interstitial material with ordered arrays of inclusion materials, where the interstitial and inclusion materials have differing permittivity and permeability characteristics. Alternatively, magneto-dielectric materials in the form of sheets are known. Such materials, however, do not provide isotropic effects, which greatly limits their utility in RF lenses and antennas. Similarly, in the case of particulate materials the surrounding milieu is often non-uniform in regards to magneto-dielectric materials, resulting in a loss of focus in smaller resonance frequency bands.
It should also be appreciated that such devices display only dielectric properties, where the use of a material that has both magnetic and dielectric properties can provide advantages over material with only dielectric properties, especially when used for antenna applications (for example for phase shifters).
Thus, there is still a need for an effective magneto-dielectric material that minimal dielectric losses.